Greasy Fork is available in English.
Support for over 70 sites! Loads manga chapter into one page in a long strip format, supports switching chapters, minimal script with no dependencies, easy to implement new sites, loads quickly and works on mobile devices through bookmarklet
Mangadex.org has the next chapter and previous chapter inverted
When I load the chapter the next chapter is actually the previous chapter and vice versa. So I just inverted the functions to make it work. Just letting you know in case you want to modify it.